Abstract

Northeast of Caicos Island (Bahamas) a large sedimentary ridge rises from the deep sea floor. This asymmetrical ridge is steepest on the south side and lies parallel to the Bahama Banks. Four 6-m-long cores taken from 2850 to 2900 fathoms consist predominantly of pelagic clays (illite and chlorite); they contain interbedded calcarenites which consist of foraminifera (benthonic and pelagic), pteropods from both neritic and littoral depths (indicating considerable displacement of fauna), and finer material. Primary structures such as graded bedding, cross bedding, convolute bedding and parallel bedding are observed in these beds. Considerable mechanical sorting of faunal species produced two distinct sediment facies, the lower consisting of foraminifera and pteropod tests and the upper of clay, discoasters, and coccoliths.

A single stratigraphic sequence is seen in the four cores. Each core exhibits similar variation in carbonate content, similar sequence of manganese-stained layers, and a similar sequence of sediment colors. One apparently correlative calcarenite thins from 58 cm to 28 cm and the mean grain size decreases from 0.17 mm to 0.012 mm, as distance from the Bahama Banks increases by 100 miles.

The Caicos Outer Ridge consists predominantly of clays evidently deposited by a southeasterly flowing deep ocean current. Incorporated in this lutite ridge are calcarenites which originated on the Bahama Banks and spread along the ridge and onto the surrounding abyssal plains.

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